You may need to keep running the exe to force the dialog to appear between tests, until whatever is blocking Opus accessing the internet (or DNS, at least) is working again.
In the next update we have a fix coming for that issue, where if the update check is triggered automatically (due to not being run in a while) and then gets stuck, you're then unable to make the dialog appear. The exe I posted works around that issue for now, and the underlying problem is that something is preventing Opus (dopus.exe) from accessing the internet.
Presumably the FTP functionality in Opus is also not working, if you try with a public FTP site (e.g. ftp.demon.nl).
Make sure nothing is turned on in Preferences / Internet / Proxy as well, unless you need to use a proxy.
After making changes to firewall/security/network configuration, I'd recommmend fully exiting Opus (via File / Exit Directory Opus) before testing again.